The objective of the proposed research is to determine mechanisms by which mammalian reovirus nonstructural protein s1s promotes systemic viral dissemination. Previous studies and preliminary data indicate that the s1s protein functions in reovirus- induced cell cycle arrest and apoptosis. However, it is not known whether these processes are responsible for s1s-mediated reovirus spread in the infected host. The central hypothesis of these studies is that the s1s protein inhibits host cell cycle progression, leading to apoptotic cell death. Subsequently, apoptotic cells are engulfed by phagocytic cells that transport the virus from the site of inoculation to peripheral organs that support secondary viral replication. Two integrated specific aims are proposed to determine how s1s contributes to reovirus-induced cell cycle arrest, apoptosis, and systemic spread. The first specific aim will define sequences in s1s required for cell cycle perturbation and apoptosis induction, and identify cellular factors involved in disrupting cell cycle progression in response to reovirus infection. The second specific aim will determine the role of s1s-mediated cell cycle arrest and apoptosis in systemic reovirus dissemination in vivo. Collectively, these studies will contribute broadly to viral pathogenesis research by enhancing an understanding of the molecular and cellular bases of viral dissemination, and provide important new insights into mechanisms by which viral infection modulates the host cell cycle and culminates in disease. My near-term career goal is to obtain a position at a college or university where I will lead my own research team. I am currently applying for academic positions and hope to attain a suitable opportunity within the next academic year. I look forward to becoming an independent investigator and building my research team. I will begin by applying for research grants, including an investigator-initiated R01 application. This application for a K22 career development award has been submitted to improve the prospects of achieving both of these goals. The training I have received to this point in my career has prepared me well for the transition from postdoctoral fellow to independent laboratory team leader. This award would enhance the possibility of obtaining a tenure-track faculty position and provide funds to generate preliminary data that will form the foundation of future grant applications. Public Health Relevance: The goal of the experiments described in this proposal is to determine how cell cycle arrest and apoptosis mediated by the reovirus s1s protein contribute to viral pathogenesis. Findings from these studies could lead to new insights into these processes that play fundamental roles in development, immunity, and cancer. Such insights might lead to new treatments for degenerative, immunologic, or neoplastic diseases.